Re: problem with C++ sort algorithm
Joel Eidsath wrote:
jo_atman@yahoo.com wrote:
bool compareByCloseAndAlloc( State* s1, State* s2 )
{
int retVal = s2->getPDClose() - s1->getPDClose();
if ( retVal != 0 ) return retVal < 0;
return s1->getAllocation() - s2->getAllocation();
}
Well, this guy asked me why i'm returning a boolean (retVal < 0) on
line 2, but an integer on line 3. I said, well, C++ really uses ints as
bool, and that i could change the code to
bool compareByCloseAndAlloc( State* s1, State* s2 )
{
int retVal = s2->getPDClose() - s1->getPDClose();
if ( retVal != 0 ) return retVal < 0;
retVal = s1->getAllocation() - s2->getAllocation();
return retVal < 0;
}
but it wouldn't make a shred of a difference. And it did. It fixed the
problem.
Possibly because your boolean algebra is faulty.
If x is greater than y, then: x - y is true, x - y < 0 is false
If x is equal to y, then: x - y is false, x - y < 0 is false
If x is less than y, then: x - y is true, x - y < 0 is true
And that in turn means the original was not a Strict Weak Ordening.
(Just stating the obvious probably, but that is what really kills the
sort)
HTH,
Michiel Salters
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